In a standard transmission, a mainshaft is journalled to an input shaft via a pocket bearing. The latter bearing has been traditionally difficult to lubricate because of its relatively concealed position within a bore in the end of the input shaft.
Conventional devices for providing pocket bearing lubrication have included port holes, grease packs, oil slingers, and hydraulic pumps. Port holes generally are machined radially through transmission input shafts for ducting oil inwardly to pocket bearings. Grease packs are simply large masses of grease in which pocket bearings are packed during assembly of transmissions. Oil slingers and hydraulic pumps involve mechanical pumping actions for providing forced oil flow to pocket bearings.
Port holes have been found deficient in high speed lubrication of transmission input shafts because oil travels inwardly to the pocket bearings only during slow rotation or stoppage of the shaft. At high rotation speeds, centrifugal force throws the oil outwardly rather than inwardly through the port holes, thus starving the bearing at high speeds when lubrication becomes more critical.
Grease packs have been successful at low speeds and under low loading conditions. However, under increased speed and loading conditions grease packs deteriorate rapidly and are, therefore, unsuitable for long-term bearing lubrication.
Operationally, oil slingers and hydraulic pumps have been more successful than port holes and grease packs. However, slingers have tended to be less efficient in the high speed-high load conditions of today's heavy duty transmissions and most hydraulic pumps are generally considered too complex and expensive as a feasible alternative.